Patterning of nanostructures

ABSTRACT

A technique for forming nanostructures including introducing a plurality of molecular-size scale and/or nanoscale building blocks to a region near a substrate and simultaneously scanning a pattern on the substrate with an energy beam, wherein the energy beam causes a change in at least one physical property of at least a portion of the building blocks, such that a probability of the portion of the building blocks adhering to the pattern scanned by the energy beam is increased, and wherein the building blocks adhere to the pattern to form the structure. The energy beam and at least a portion of the building blocks may interact by electrostatic interaction to form the structure.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/347,662, filed Jan. 10, 2012, now U.S. Pat. No. 8,937,001,issued Jan. 20, 2014, which is a divisional application of U.S. patentapplication Ser. No. 10/444,176, filed May 23, 2003, now U.S. Pat. No.8,093,144, issued Jan. 10, 2012, which claims the benefit of U.S.Provisional Application Ser. No. 60/383,396, filed May 24, 2002, theentire disclosures of which are each herein incorporated by reference intheir entirety.

FIELD OF THE TECHNOLOGY

The present invention relates to the fabrication of two- andthree-dimensional functional structures with a characteristic lengthscale below 100 nanometers (nm).

BACKGROUND

Presently there is great interest in the fabrication of functionalsemiconductor devices with length scales below 100 nm, i.e.,nanoelectronics. The laws of physics allow, in theory, the building oflogic devices such as transistors with characteristic length scales onthe order of about 1 nm. Reaching these limits, however, is difficultand expensive.

Methods for fabricating devices below 100 nm include both top down andbottom up approaches. Conventional top down approaches such asphotolithography or electron beam lithography utilize formation andselective removal of various levels to form functional devices. Top downprocesses are very expensive for devices with features below 100 nm. Inaddition, such methods can generally be used only to buildtwo-dimensional logic, typically on a planar silicon wafer, andhistorically have followed Moore's law yielding only a factor of twoincrease in device density every 18 months.

Direct-write top down approaches have included atomic force microscopy(AFM) direct writing of liquids, i.e., dip pen nanolithography andscanning tunneling microscopy (STM) writing of oxides and chargereplicas. These methods suffer from slow speeds, lack of a general setof building materials for fabricating electronic components, and aconstraint to two-dimensional structures.

Tools for creating three-dimensional structures employ, for example,electron beam and ion beam decomposition of chemical vapor precursors.Such tools have been useful in mask and chip repair and have been shownto be capable of writing three-dimensional structures. Typically,organometallic precursor gases adsorbed onto substrate surfaces aredecomposed using energy supplied from incident beams, depositing thedesired metal or insulator. This technique facilitates deposition ofnanometer- to micrometer-size structures with nanometer precision inthree dimensions and without supplementary process steps such aslift-off or etching procedures. Although successful in creating highresolution three-dimensional structures, both scanning electronmicroscopy (SEM) and focused ion beam (FIB) chemical vapor deposition(CVD) suffer from significant contamination by the organic components ofprecursor gases. Carbon contamination from typical precursor gases mayexceed 50%, thus altering device conductivities to levels unacceptablefor many desired applications. Device fabrication by energetic-beam CVDis also constrained by an inherently small number of available precursorgases, thus limiting the variety of materials that can be deposited.Finally, because existing processes are serial and sufficient beamenergy must be applied to decompose the precursor, deposition speeds arevery slow.

In bottom up approaches, layers are selectively applied to (rather thanremoved from) a substrate. For example, nano-scaled building blockssynthesized precisely by chemistry or other methods may later beassembled by, e.g., self assembly. Presently the complexity of logicwhich may be built in this way is extremely limited.

Nature is excellent at predicated assembly of complex molecules such asDNA on a scale similar to that of present-day nanostructures. Nature canmake precise molecules with enzymes such as polymerase that typicallyhave extremely low error rates by utilizing feedback and performingerror correction. However, direct feedback and error correction areseldom implemented in present fabrication processes, and hence the yieldof functional devices is low in comparison to functional moleculesformed by biological processes.

SUMMARY

The present invention facilitates a precise and rapid patterning of veryhigh purity nanoscale building blocks in two and three dimensions inorder to build functional ultrahigh density devices.

In an aspect, the invention features a method for forming a feature, themethod including forming a charge pattern on a substrate, the chargepattern having a first type of charge. The method also includesintroducing a plurality of at least one of molecular size-scale andnanoscale building blocks to a region proximate the charge pattern, thebuilding blocks having a second type of charge and adhering to thecharge pattern to form the feature.

One or more of the following features may be included. The buildingblocks may be at least one of ions, nanoclusters, nanoparticles, andorganic molecules. The charge pattern may be formed with an energy beam,such as an ion beam, an electron beam, or a photon beam. The adherednanoclusters may be globally sintered. The nanoclusters may be less than100 nm in overall dimension. The nanoclusters may be introduced bydusting. The nanoclusters may be directed toward the substrate as astream, such that the nanoclusters adhere only to the charge pattern. Avelocity of the plurality of nanoclusters may be controlled. Thevelocity of at least a portion of the plurality of nanoclusters may bereduced in the region proximate the charge pattern. The velocity of atleast a portion of the plurality of nanoclusters may be controlled by anelectric field that may be alternating. The velocity of at least aportion of the plurality of nanoclusters is controlled by a magneticfield that may be alternating. The velocity of at least a portion of theplurality of nanoclusters is controlled by a charged aperture disposednear the substrate.

The first type of charge may be positive or negative. The second type ofcharge may be positive, negative, or neutral.

The charge pattern may include a dot and at least one nanocluster mayadhere to the dot to form an initiation site for a nanowire. A precursormay be introduced to a region proximate the initiation site to initiategrowth of the nanowire.

In another aspect, the invention features a method for forming astructure, the method including defining a charge pattern by an energybeam; and correcting an error in the charge pattern.

One or more of the following features may be included. Correcting theerror in the charge pattern may include providing a feedback loopcomparing a set of charge data to data corresponding to a desired chargepattern. The charge pattern may have a first type of charge, the errormay include a misplaced charge, and correcting the error may includedischarging the error with a second beam having a second type of charge,such as an ion or an electron beam. A plurality of nanoclusters may beintroduced to a region proximate the charge pattern, the nanoclustershaving the second type of charge and adhering to the charge pattern todefine the structure, and the error may be corrected after the chargepattern is formed and before the plurality of nanoclusters isintroduced. The error may include a missing charge in the charge patternand correcting the error may include adding a charge to the chargepattern with the energy beam.

In another aspect, the invention features a method for forming astructure, including introducing a plurality of at least one ofmolecular-size scale and nanoscale building blocks onto a surface of asubstrate to form the structure; and correcting an error in thestructure.

One or more of the following features may be included. Correcting theerror in the structure may include providing a feedback loop comparing aset of charge data to data corresponding to a desired structure.Correcting the error may include performing an additive correction.Correcting the error may include depositing a charge on the substrateand introducing at least one additional building block to a regionproximate the charge. Correcting the error comprises performing asubtractive correction, which may include removing a portion of thestructure with, e.g., a beam.

In another aspect, the invention features a method for forming afeature, including introducing a plurality of at least one ofmolecular-size scale and nanoscale building blocks to a region proximatea substrate; and simultaneously scanning a pattern on the substrate withan energy beam. The energy beam causes a change in at least one physicalproperty of at least a portion of the building blocks such that aprobability of the portion of the building blocks adhering to thepattern scanned by the energy beam is increased.

One or more of the following features may be included. The energy beammay include at least one of an electron beam and an ion beam. The changein the physical property may be caused by direct collision between theenergy beam and the portion of the building blocks. The change in thephysical property may be caused by sintering. The energy beam may sinterthe portion of the nanoclusters by heating at least a portion of thesubstrate proximate the portion of the nanoclusters.

In another aspect, the invention features a method for forming afeature, the method including introducing a plurality of at least one ofmolecular-size scale and nanoscale building blocks to a region proximatea substrate, and simultaneously scanning a pattern on the substrate withan energy beam. The energy beam and at least a portion of thenanoclusters interact by electrostatic interaction to form the featureon the substrate.

In another aspect, the invention features a method for creating a chargeretention layer. The method includes providing a substrate, adsorbing athin layer of a gas onto a surface of the substrate to create the chargeretention layer; and defining a charge pattern on the thin adsorbedlayer.

One or more of the following features may be included. The thin layermay have a thickness of one monolayer. The adsorbed gas may be an inertgas, such as xenon. The inert gas may be adsorbed at a low temperature.The adsorbed gas may include a hydrocarbon vapor. Adsorbing thehydrocarbon vapor may include cracking and depositing the hydrocarbonvapor.

In another aspect, the invention features a method for forming astructure, the method including providing a substrate, defining a firstregion of the substrate having a charge of a first type, defining asecond region of the substrate having a charge of a second type; anddusting the first and second substrate regions with a plurality of atleast one of molecular-size scale and nanoscale building blocks having acharge of the second type. The building blocks are repelled from thefirst substrate region and attracted to the second substrate region.

One or more of the following features may be included. A charge patternmay be formed on the substrate, the charge pattern having the secondtype of charge and a second plurality of at least one of molecular-sizescale and nanoscale building blocks may be introduced to a regionproximate the charge pattern, the nanoclusters having the first type ofcharge, the nanoclusters adhering to the charge pattern.

In another aspect, the invention features a method for forming afeature, the method including creating a virtual mask on a substrate anddepositing a monolayer on a region of the substrate substantially freeof the virtual mask to form the feature.

One or more of the following features may be included. Creating thevirtual mask may include scanning an energy beam, such as an ion beam,in a pattern on the substrate. Depositing the monolayer may includeatomic layer deposition.

A nanostructure may be defined on the substrate, and a gap may bedefined in the nanostructure with the gap initially having a firstlength. The monolayer may be deposited over the nanostructure and thegap, and after the deposition of the monolayer, the gap may have asecond length, the second length being less than the first length.

In another aspect, the invention features a system including adeposition chamber. Disposed within the deposition chamber, a beamsource is arranged to form a charge pattern on a substrate placed withinthe deposition chamber. A molecular size-scale building block (MSSBB)source is disposed outside the deposition chamber, the MSSBB sourcearranged to introduce a plurality of at least one of MSSBBs andnanoscale building blocks to a region proximate the charge pattern. Thedeposition chamber, beam source, and MSSBB source are capable of beingmaintained at a vacuum.

One or more of the following features may be included. A feedbackmonitoring system may be in electrical communication with the beamsource and the MSSBB source, for correcting errors caused by at leastone of the beam source and the MSSBB source.

In another aspect, the invention features a system including adeposition chamber. Disposed within the deposition chamber is a beamsource arranged to form a charge pattern on a substrate placed withinthe deposition chamber. An MSSBB source is disposed outside thedeposition chamber, the MSSBB source arranged to introduce a pluralityof at least one of MSSBBs and nanoscale building blocks to a massselector. A mass selector is disposed in fluid communication with theMSSBB source. The mass selector is capable of introducing a plurality ofat least one of MSSBBs and nanoscale building blocks having apre-determined mass and charge to a region proximate the charge pattern.The deposition chamber, beam source, MSSBB source, and mass selector arecapable of being maintained at a vacuum.

The following feature may be included. A feedback monitoring system maybe in electrical communication with the beam source, the MSSBB source,and the mass selector, for correcting errors caused by at least one ofthe beam source, the MSSBB source, and the mass selector.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing discussion will be understood more readily from thefollowing detailed description of the invention, when taken inconjunction with the accompanying drawings, in which:

FIGS. 1( a)-(c) are schematic diagrams of an electron beam-basednanopatterning process for writing a charge pattern;

FIGS. 2( a)-(c) are schematic diagrams of an ion beam-basednanopatterning process for writing a charge pattern;

FIG. 3 is schematic diagram illustrating deposition of nanoclusters withcharge masking;

FIGS. 4( a)-(c) are schematic diagrams of various configurations ofelectric and magnetic fields for manipulating the velocities of chargednanoclusters;

FIGS. 5( a)-(b) are schematic diagrams of fabrication by rapidlyalternating between the charging and dusting processes;

FIGS. 6( a)-(c) are schematic diagrams of deposition on conductivesubstrates using charged hydrocarbon vapors;

FIG. 7 is a schematic diagram of an electron beam based nanopatterningprocess with direct beam energy sintering of nanoclusters;

FIG. 8 is a schematic diagram of an ion beam based nanopatterningprocess with direct beam energy sintering of nanoclusters;

FIGS. 9( a)-(d) are schematic diagrams of a structure formed by atomiclayer deposition;

FIGS. 10( a)-(c) are schematic diagrams of a process for creatingnanowires;

FIGS. 11( a)-(d) are schematic diagrams of an atomic layer depositionprocess for creating very thin gaps;

FIG. 12 is a schematic diagram of a fabrication process utilizingalternating organic molecule and inorganic nanocluster layers;

FIGS. 13( a)-(c) are schematic diagrams of electron beam based chargenanopatterning processes with multiple beams running in parallel;

FIG. 14 is a schematic diagram of a method for generating an array ofparallel electron beams by a micro-mirror array and a photocathode;

FIG. 15 is a schematic diagram of error correction performed by acombination of positive ion and negative electron or ion beams;

FIG. 16 is a schematic diagram illustrating a feedback process; and

FIG. 17 is a schematic diagram illustrating a system combining a chargedion or electron beam source, a molecular size-scale building block(MSSBB) source for introducing at least one of MSSBBs and nanoscalebuilding blocks, mass and charge selection apparatus, and other vacuumcomponents.

Like referenced features identify common features in correspondingdrawings.

DETAILED DESCRIPTION

In one approach for patterning nanoscale building blocks, arbitrarythree-dimensional nanostructures of high purity are formed by rapidlycreating a charge pattern of nanoscale dimensions on a substrate using ascanning beam, generating very high purity molecular size-scale buildingblock (MSSBB) of a first type that image the charge pattern, andsintering the MSSBBs to form a locally solid layer delineated by thecharge pattern by an additional global heating source. In someembodiments, nanoscale building blocks (NSBB) may be used to image thecharge pattern. MSSBBs or NSBBs may be any one of organic molecules,such as nucleotides, amino acids, or self-assembling monolayers, ions,nanoclusters, and nanoparticles. In a preferred embodiment, MSSBBs arenanoclusters, which may have dimensions ranging from 0.2 nm to more than100 nm. More specifically, when the nanoclusters are introduced inproximity to the charge pattern, the nanoclusters are attracted to thepattern, thereby “imaging” the charge pattern. A charged nanocluster isattracted to its opposite charge on a surface of the substrate. Neutralparticles may also be attracted by induced dipoles. The process isrepeated with nanoclusters of a second type to create arbitrarythree-dimensional nanostructures. In addition to inorganic nanoclusters,organic molecules which have an affinity for a charge pattern or whichthemselves can be charged and thus have an affinity for a charge patternmay also be similarly patterned. The charge pattern may be created andrepresented digitally, or it may be used to control the action of thescanning beam. In some embodiments, aerosols may be used to developcharged surfaces for xerography [see, e.g., J. T. Bickmore, inXerography and Related Processes, edited by J. H. Dessauer and H. E.Clark (Focal Press, New York, 1965) Chap. 11, p. 309, incorporatedherein by reference].

An alternative approach to creating arbitrary three-dimensionalnanostructures of high purity involves globally dusting a surface withnanoparticles, sintering selected regions with a scanning energy beam,removing unsintered nanoparticles by, e.g., a supercritical carbondioxide (CO₂) etch, and repeating the procedure.

Both approaches may be used to create electronic structures ab initio orto place additional components on a pre-existing semiconductor chip madeby conventional (e.g., photolithographic) methods.

This process is highly versatile in comparison to existing technologiesbecause of, inter alia, the wide variety of materials that may bemagnetron sputtered to form the nanoclusters, such as metals, inorganicsemiconductors, and insulators. The range of sputtered materials ishigher than the number of existing precursor gases. Also, in contrast tosome top-down approaches, these nanoclusters do not require an organiccapping group, and fabricated devices, therefore, are nearly 100% pure.

In alternative embodiments, other patterning methods are possible whichmay give higher resolution. For example, instead of patterning solelynegative charges, negative charges as well as positive charges in areasmay be patterned in distinct areas using a dual-beam, scanning electron,and/or focused ion beam source.

Referring to FIGS. 1( a)-(c), nanoscale structures are fabricated bynanoelectrography. An energy beam, such as an electron beam 110 may beused for the fabrication of features having nanoscale dimensions. Insome embodiments, the energy beam may be an ion beam or a photon beam.Electron beam 110 may have a first type of charge, i.e., a negativecharge, and may be generated by an electron beam source 112, e.g., anenvironmental scanning electron microscope (ESEM) such as the XL-30Esem-FEG manufactured by FEI Company, Hillsboro, Oreg. Electron beam 110may be deflected by electrostatic steering plates (not shown). Electronbeam 110 writes a charge pattern 120, also referred to as a chargereplica, onto a substrate 130. In the embodiment shown in FIG. 1( a),the pattern is negatively charged. Substrate 130 may be formed of, forexample, an electret, i.e., a dielectric material capable of storingcharge, such as mylar, poly(methylmethacrylate), SiO₂, or CaTiO₃.Substrate 130 may be square with sides 132, 134 having a length l₁ of,e.g., 1 centimeter (cm) and a width w₁ of, e.g., 1 cm, respectively.Substrate 130 may be obtained from, for example, Goodfellow Corporation,based in Pennsylvania. In some embodiments, an ion beam [see, e.g.,Fudouzi et al., Adv. Mater 14 1649 (2002), incorporated herein byreference, who use a 30 keV Ga⁺ ion beam to write positively chargedpatterns in CaTiO₃], an atomic force microscope (AFM) writing head [see,e.g., P. Mesquida and A. Stemmer, Adv. Mater. 13 1397 (2001),incorporated herein by reference, who induce negative or positive chargepatterns in poly(tetra-fluoroethylene) (PTFE) by applying voltage pulsesof ±15-20V to the tip], microcontact stamping of charge [see, e.g., H.O. Jacobs and G. M. Whitesides, Science 291 1763 (2001), incorporatedherein by reference, who have been working toward submicron trapping ofcharge in thin layers of PMMA on n-doped silicon by applying 10-20 Vbetween the conductive silicon support and a patterned gold-coatedpoly(dimethylsiloxane) stamp], may be used to generate charge pattern120.

Referring to FIG. 1( b), a plurality of nanoclusters 140, here shown tobe positively charged, are introduced to a region 145 proximate chargepattern 120. Passing by the charge pattern 120, nanoclusters 140 areattracted to the substrate 130 and adhere to negatively chargedsubstrate surface 135, forming a patterned feature 150. In someembodiments, a plurality of MSSBBs may be introduced to region 145, andmay adhere to substrate surface 135 to form feature 150.

Nanoclusters 140 may be generated by an MSSBB or NSBB source such as theNC200-UHV Gas Condensation Nanocluster Source manufactured by OxfordApplied Research (not shown). This apparatus includes a DC-magnetronbased sputtering source that forms nanoclusters 140 by condensing atomsof sputtered material within a cooled aggregation region and thensweeping them from the device on a laminar flow of argon and/or helium.Nanoclusters may be neutral, negative, or positively charged.Nanoclusters may be filtered to introduce nanoclusters of a specificmass or charge by a mass and charge selection apparatus such as a QMF20Mass Quadrupole filter available from Oxford Applied Research (notshown). Nanoclusters are positively charged in the embodiment shown inFIG. 1( b).

In some embodiments, a matrix-assisted laser desorption ionization(MALDI) mass spectrometry source is used as an MSSBB or NSBB source. Anexample of a suitable MALDI mass spectrometery source is, e.g., theProfiler MALDI-TOF mass spectrometery system manufactured by StanfordResearch Systems, Sunnyvale, Calif. The MALDI mass spectrometry sourcecreates charged fragments from larger molecules. The larger moleculesare typically organic molecules, such as nucleotides, amino acids, orself-assembling monolayers. This mass spectrometery source can filterout a specific charged species of appropriate mass and direct it towardsthe charged surface. This approach may be used to, for example, build agene chip of very high density. Examples of other suitable sourcesinclude, for example, cesium-doped negative sputter ion beam sourcessuch as one manufactured by Plasmion (formerly Skion) TechnologyCorporation, or an ionized beam K-cell, such as the IBE1 or IBE10Ionised Beam K-cell manufactured by Oxford Applied Research. An MSSBB orNSBB source may also be an ion source for small atomic-layer epitaxy(ALE) precursors such as ZnCl₂ and H₂S. Ions of these ALE precursors maybe prepared in an ion source and then directed to charged pattern 120 tocreate monolayers of the ALE precursor to enable subsequent spatiallypatterned ALE.

The sputtered material from which nanoclusters 140 are formed may be ametal such as copper (Cu) or aluminum (Al); an inorganic semiconductorsuch as silicon (Si), germanium (Ge), indium phosphide (InP), galliumarsenide (GaAs); and an insulator such as silicon dioxide (SiO₂). Suchnanoclusters may emerge from the MSSBB or NSBB source having a secondtype of charge, i.e., positive, negative, or neutral, and may beseparated by electrostatic separation plates. In an embodiment,nanoclusters 140 are positively charged. Nanoclusters 140 may have adiameter selected from a range of 0.2 nm to greater than 100 nm.Preferably, nanoclusters 140 are less than 100 nm in overall dimension.

Referring to FIG. 1( c), nanoclusters 140 are sintered into a bulkmaterial, e.g., a monolayer, by, for example, a peltier heating stage.Peltier heating stages are thermoelectric modules that provide heatglobally upon application of a low voltage DC power. Sintering of, e.g.,2 nm diameter silver (Ag) nanoclusters, is performed at approximately300° C. An alternative global sintering device, such as a laser, mayalso be employed. The steps of forming charge pattern 120, introducingnanoclusters 140, and sintering nanoclusters 140 may be repeated to formseveral adjacent monolayers.

Referring to FIGS. 2( a)-(c), an alternative approach tonanoelectrography may be used for fabricating nanoscale structures. Afocused ion beam of positive ions 210 delivered from, for example, aStrata™ DB235 source manufactured by FEI Company, writes a positivecharge pattern 220 onto substrate 130. In an embodiment, nanoclusters140 are negatively charged. A plurality of negatively chargednanoclusters 140, filtered via a selection apparatus from thenanocluster source (not shown), pass over the charge pattern 220, areattracted to the positively charged charge pattern 220 on substrate 130,and adhere to substrate 130. The velocity of the nanoclusters 140 may bemanipulated via electric and magnetic fields, e.g., in accordance withthe methods described below with reference to FIGS. 4( a)-4(c).Referring to FIG. 2( c), nanoclusters 140 are sintered into a bulkmaterial by global heating provided from a source such as a peltierheating stage (not shown) or laser (not shown) to form a feature 230.

Referring to FIG. 3, several embodiments of charge patterning arepossible, including negative or positive charge masking in whichnanoclusters of one charge are repelled from regions of like charge, andnanoclusters of neutral charge or opposite charge are attracted to themask. For example, a first charge pattern 310 having a charge of a firsttype, e.g., positive, may be formed on a first region of a substrate by,e.g., a positive ion beam (not shown). First charge pattern 310 may besurrounded by a second region of the substrate, e.g., second chargepattern 320 having a charge of a second type, e.g., negative. Thesubstrate may be dusted with a plurality of at least one of MSSBB andnanoscale building blocks, such as nanoclusters 140, having a charge ofthe second type, e.g., negative. Negatively charged nanoclusters 140,filtered by a selection apparatus (not shown), are strongly attracted topositive charge pattern 310 and are less likely to deposit on substrateregions defined by the negative charge pattern 320. A similar effect maybe achieved by reversing polarities such that first charge pattern 310has a negative charge, second charge pattern 320 has a positive charge,and nanoclusters 140 has a positive charge, so that positively chargednanoclusters 140 are strongly attracted to positive charge pattern 310and are less likely to deposit on regions defined by the negative chargepattern 320.

Referring to FIGS. 4( a)-4(c), the kinetic energy of nanoclusters 140may also be manipulated by subjecting charged nanoclusters 140 toelectric and magnetic fields. Appropriately placed, such fields maydecrease or increase the velocity of nanoclusters 140 having a desiredcharge, thereby increasing the likelihood of the species adhering to acharge pattern 420. For example, to increase the probability of chargednanoclusters 140 being attracted and adhering to negatively chargedcharge pattern 420, the velocity of positively charged nanoclusters 415may be decreased. The probability of attraction and adherence of thesenanoclusters 140, therefore, may be manipulated by controlling thekinetic energy of the nanoclusters via electric or magnetic fields.

More particularly, referring to FIG. 4( a), nanoclusters 140 having aspecific charge may be selected by introducing an opposing fieldincident to a nanocluster beam 412. In an embodiment, positively chargednanoclusters 140 may be used to develop a negative charge pattern 420 insubstrate 130 to form a patterned feature (not shown). Nanoclusters 140have an initial velocity and travel incident to a conducting plate 430.Conducting plate 430 may include a conducting material such as, forexample, copper. Conducting plate 430 may held at a positive potentialto slow down incident positive nanoclusters. At an appropriatepotential, a velocity of a portion 415 of nanoclusters 140 approacheszero, thus increasing the influence of the electric field of chargepattern 420 on the portion 415 of nanoclusters 140. This potential maybe determined by utilizing an ion gauge to measure the number ofdeposited positive nanoclusters 140, and the zero velocity conditionwould be met when the ion gauge counts zero particles. The polarities ofconducting plate 430, charge pattern 420, and nanoclusters 140 may bereversed to achieve a similar effect, e.g., conducting plate 430 andnanoclusters 140 may have a negative potential, and charge pattern 420may be positively charged.

Referring to FIG. 4( b), electric and magnetic fields used formanipulating the energies of nanoclusters 140 may also alternate, forexample, in the radio frequency regime. Initially high energy, chargednanoclusters 140 may be trapped in an alternating field 440 generatedby, for example, an alternating current (AC) power supply, leading to ahigh-density of zero-velocity particles 415 within alternating field440. In an embodiment, a vacuum chamber (not shown) housing ahigh-energy patterning beam of, e.g., electrons or ions, may also havean appropriate electrode configuration for generating alternating field440 for trapping nanoclusters 140. After charge pattern 420 is written,the cluster beam may be initiated and nanoclusters 140 with a desiredcharge, i.e., a charge different from the charge of the charge pattern,may be subsequently trapped directly above charge pattern 420. Theportion 415 of charged nanoclusters 140 having a velocity of zero wouldthen be attracted to a localized electric field generated by chargepattern 420.

Referring to FIG. 4( c), other measures may also increase the likelihoodof charged nanocluster 140 deposition. For example, a conducting wireaperture 450 may be held at a negative potential. Substrate 130, havinga negative charge pattern 420 is mounted in a center portion of aperture450. Positively charged nanoclusters 140 from a cluster beam 412 areattracted to conducting wire aperture 450. Positively chargednanoclusters 140 will be influenced at longer distances, e.g., 10 cm bythe negative potential of wire aperture 450, but as they approach wireaperture 450, charged nanoclusters 460 are attracted to the smallerlocal field of the negatively charged charge pattern 420. A similareffect may be achieved by patterning a large aperture feature (notshown) directly into substrate 130, and patterning finer features in thecenter of the aperture. Such effects may also be seen by reversing thepolarities of the aperture 450, charge pattern 420, and nanoclusters140. Charged aperture 450 may be used in conjunction with any of themethods described above with reference to FIGS. 1 to 8, 10, 13, 15, and16 for reducing the velocity of the desired charged nanoclusters 140.

The fidelity of patterned features, such as patterned feature 150 [seeFIG. 1( c)], may be improved by alternating between charging and dustingprocesses. An exact amounts of charge may be placed onto an electretsubstrate 130 by knowing the charge retention capability of thesubstrate and by controlling the current of the beam used to create thecharge pattern. A cluster counting scheme similar to “channeltron” ioncounting may be incorporated, whereby nanoclusters introduced into achamber in which the substrate is disposed may be counted, with anaccuracy on the order of a single nanocluster. A channeltron single iondetector may be used to count the number of nanoclusters generated. Sucha detector could be, for example, the Channeltron Mass Spec Detectormade by Burle Technologies Inc. This method is widely used for iondetection, but may also be used for nanocluster detection. Chargednanoclusters are focused to the channeltron detector. A nanoclusterstriking the detector generates secondary electrons that have anavalanche effect to create more electrons. Eventually, sufficientsecondary electrons are generated to induce a pulse. The transmittedcurrent from the detector is directly proportional to the number ofnanoclusters hitting the detector. With this count, one may calculatethe deposition rate of the nanoclusters, thereby calculating the timenecessary to dust the substrate with an approximate number ofnanoclusters with charge equal and opposite to the charge on thesubstrate. A high-speed shutter or set of electrostatic plates (notshown) may be used to shut off the cluster beam when the desired numberof nanoclusters have been shot. The nanoclusters deposit on patternedcharged regions. This process also neutralizes any charge present on thesubstrate and prepares it for the next alternation between charging anddusting. This alternation may be done at high frequencies to rapidlygenerate features of interest.

Referring to FIGS. 5( a)-5(b), nanostructure fabrication may be carriedout by alternating between charging and dusting processes as follows. Ascanning beam 510 may put down a line of charge 520 on substrate 130. Inan embodiment, scanning beam 510 may define a point of charge, thecharge being of a first type, e.g., negative. Referring to FIG. 5( b),substrate 130 with charge line 520 may be dusted with nanoclusters 140having a polarity of a second type opposite to that of charge line 520,e.g., positive. An MSSBB or NSBB source such as a Nanocluster Sourcefrom Oxford Applied Research 530 may be used to eject nanoclusters 140.

A cluster source gate 540, disposed between cluster source 530 and adeposition chamber (not shown) in which substrate 130 is disposed,remains closed during charge writing. Then, after a charge pattern, suchas charge line 520 is defined, gate 540 is opened and clusters 140 aredeposited onto substrate 130 to form a pattern defined by charge line520. In some embodiments, in addition to gate 540, another mass orcharge selector may be employed to eject nanoclusters 140. For example,a mass quadrupole such as Oxford Applied Research's QMF200 QuadrupoleMass Filter (not shown) may be used to provide nanoclusters 140 having aspecified mass and charge. A Channeltron 550 may be used to gauge adeposition time required to release a specific number of nanoclusters140. After charge line 520 is written, the cluster source 530 may beoperated for the calculated deposition time to deposit a desired numberof nanoclusters 140.

In some embodiments, a substrate on which a charge pattern is writtenmay be formed from a conductive material, such as gold, and, therefore,charge pattern may dissipate after it is defined. Here, one or severalmonolayers of adsorbate, such as an inert gas that is physicallyadsorbed at low temperature or a self-assembling monolayer, may bedeposited onto the substrate in order to retain the charge pattern. Uponsintering, the inert adsorbate may enter the gas phase and not becomepart of the final structure formed on the conductive substrate. A verythin layer, e.g., one or several monolayers, of an inert gas such asxenon may be also be employed. Such a gas may be adsorbed onto thesubstrate surface at a low temperature to form a charge retention layer.The charge pattern may then be written and imaged thereon.

Alternatively, hydrocarbons, such as methane or an aromatic hydrocarbonvapor may be used to assist with charge retention by forming chargeretention layers on conductive substrates. Hydrocarbon vapors, such asthose generated by colloidal graphite, may be introduced into adeposition chamber. A scanning beam may crack the vapors and depositthem selectively onto beam raster regions. Either during or subsequentto deposition, the scanning beam may be used to charge the depositedhydrocarbon vapors. Conductive substrates may then be dusted withoppositely charged nanoclusters that deposit on the charged hydrocarbonvapors. During sintering of the nanoclusters, the hydrocarbon vapors getdesorbed from the substrate surface, thereby preventing contamination ofthe substrate with hydrocarbons.

More specifically, referring to FIG. 6( a)-(c), the hydrocarbondeposition and charging approach may be used to fabricate features 600on a conductive substrate 610. Conductive substrate 610 may be madefrom, for example, gold. Referring to FIG. 6( a), a scanning beam 620cracks hydrocarbon vapors 630. Hydrocarbon vapors 630 can be introducedby a gas injection needle 640, which could be, for example, a modifiedGas Injection System sold by FEI Corp. A hydrocarbon vapor pattern 650defined by the scanning beam 620 is then formed. Referring to FIG. 6(b), scanning beam 620 charges the hydrocarbon vapors 660. Hydrocarbonvapors may be charged either during deposition or as a separate stepafter deposition. As illustrated in FIG. 6( b), charged vapors 660 maybe negatively charged. Referring to FIG. 6( c), substrate 610 is dustedwith nanoclusters 140 having a polarity opposite to that of hydrocarbonvapor pattern 660. Nanoclusters 140 are attracted to hydrocarbon vaporpattern 640, and deposit thereon to form features 670.

Physical properties of molecular-size scale and nanoscale buildingblocks, such as nanoclusters 140, may be altered by energy beams. Forexample, referring to FIG. 7, an energy beam, such as an electron beam710 delivered from a source such as an SEM, scans a pattern and directlyinteracts with nanoclusters 140, delivered from a nanocluster source,e.g., an Oxford Applied Research NC200-UHV source. This interaction maybe caused by direct collision between the energy beam and a portion ofthe building blocks, i.e., between electrons from electron beam 710 andnanoclusters 140. In an embodiment, both the cluster beam composed ofnanoclusters 140 and the electron beam 710 fire simultaneously. Electronbeam 710 thereby may change at least one physical property of at least aportion of the nanoclusters 140 such that the probability of theadherence of the portion of the nanoclusters 140 to the pattern scannedby the electron beam 710 is increased. In some embodiments the electronbeam 710 may sinter at least a portion of nanoclusters proximate asubstrate 740, forming feature 730 on substrate 740. Feature 730 may bedefined by the pattern scanned by electron beam 710. Substrate 740 maybe formed from, for example, a dielectric material like SiO₂. Sinteringrequires imparting energy from electron beam 710 to nanoclusters 140.For example, 2 nm diameter Ag clusters sinter when sufficient energy isdelivered to raise clusters to temperatures of approximately 300° C.Such energy can be imparted by direct collision between nanoclusters andelectrons, or by locally heating at least a portion of the substrate 730proximate nanoclusters 140 using the electron beam 710. Nanoclusters 140in the region proximate to energy beam 710 and the substrate 730 maythen directly sinter on the substrate forming feature 730.

Referring to FIG. 8, an ion beam 810 scans a pattern and directlyinteracts with nanoclusters 140, resulting in the alteration at leastone physical property of at least a portion of building blocks, such asnanoclusters 140, such that the probability of the adherence of theportion of the nanoclusters 140 to the pattern scanned by the ion beam810 is increased. In an embodiment, the cluster beam composed ofnanoclusters 140 and the ion beam 810 fire simultaneously. Theinteraction between ion beam 810 and nanoclusters 140 may result in achange of at least one physical property of at least a portion ofnanoclusters 140 as a result of a process such as, e.g., sintering.Material sintered by ion beam 810 may build a feature 830 on substrate840, e.g., a Si wafer. Sintering of nanoclusters 140 may occur by directcollision with ions, or by sintering due to a high local temperature ofat least a portion of substrate 840 in a region defined by ion beam 810.Feature 830 is defined by the pattern scanned by ion beam 810, to whichat least a portion of the building blocks, such as nanoclusters 140,adhere.

In an embodiment, the energy beam, such as electron beam 710 or ion beam810, may interact with at least a portion of a plurality of nanoclusters140 by electrostatic interaction to form the features 730, 830.

An alternative method for defining a nanostructure by the use of anenergy beam and a nanoscale deposition method involves the process ofatomic layer deposition (ALD), or equivalently, atomic layer epitaxy(ALE). ALD enables sequentially controlled saturating surface reactions.This process is advantageous over other forms of deposition because itallows the creation of boundaries that are atomically precise. In asimple ALD apparatus, an atomic monolayer may be created across anentire substrate. This may not be desirable. Alternatively, theaforementioned set-up for the construction of nanostructures using a FIB[see FIGS. 2( a)-(c)] may be used to create a mask on the substrate,which is populated with a monolayer in situ by ALD. The monolayer mayinclude, e.g., elements such as Zn, Cd, Hg, Mn, S, Se, Te, and As, ormetal oxides such as aluminum oxide (Al₂O₃), tin oxide (SnO₂), orindium-tin oxide (ITO) that exhibit high conductivity. An additionaladvantage of using ALD to form a monolayer is that discontinuities maybe intentionally created in the monolayer at well-defined points byfocussing an electron beam or a FIB during the ALD process. The electronbeam or FIB may locally heat an area or pattern on the substrate so thatthe thermal energy generated by the beam re-evaporates any molecules orelements that would otherwise bond with the underlying layer. If thebeam is scanned in a pattern on the substrate during the ALD process,molecules or elements may be re-evaporated at points along the pattern,creating a virtual negative mask. This process may be used to growatomically precise surfaces with cavities and discontinuities. Thesediscontinuities may be used, for example, in the area of photonics,where light can be guided in crystalline substrates along sharp anglesby using intentionally discontinuous media.

Referring to FIG. 9( a)-(d), a structure 900 is fabricated by combiningFIB and ALD. A virtual mask 910 is created by scanning the FIB in apattern on substrate 920, with enough energy in the beam to re-evaporatemolecules and break chemisorption bonds. Substrate 920 may be asemiconductor substrate such as, for example, a p-type doped siliconsubstrate. The ALD process is initiated, and monolayers are deposited onsubstrate 920 in region 930 where the FIB is not scanned. Monolayers aresequentially deposited to form a first layer 940 in region 930 until adesired thickness t₁ is achieved, e.g., 100 Å. This procedure isrepeated to deposit monolayers to form second and third layers 950, 960of different composition, to define a nanowire 970. First, second, andthird layers 940, 950, and 960 may be, for example, alternating organicand inorganic layers. This method combining FIB and ALD enablesformation of layers with atomic precision, and allows the fabrication ofstriped nanowires with atomically precise junctions, i.e., nanowireswith layers of alternating composition.

Referring to FIGS. 10( a)-(c), nanowires may be created by analternative method involving writing of charge patterns and depositionof nanoclusters. In an embodiment, the methods described above withreference to FIGS. 1( a)-5, 7, and 8 may be used to create growthinitiation sites either for nanowires (see, e.g., Hu, et al., Acc. Chem.Res. 1999, 32, 435-445, incorporated herein by reference) or nanotubes(see, e.g., Dai et al., J. Phys. Chem. B, 1999, 103, 11246-11255,incorporated herein by reference). Hu and co-workers used a nanoclustercatalyst to localize a reactant in a chemical vapor deposition processat a specific temperature that promoted vapor phase supersaturation ofthe cluster, resulting in one-dimensional growth of a single crystalnanowire. Dai and co-workers used nanocluster catalysts, such as a Fe/Mobimetallic cluster in a methane CVD process, to nucleate the growth ofsingle wall nanotubes. In an aspect of the present invention, a CVDprecursor gas is introduced into the chamber and is nucleated atinitiation sites deposited in accordance with the invention to createnanowires or nanotubes. More specifically, a charged beam of electronsor ions may write a pattern of four charged dots 1010 in substrate 130,as shown in FIG. 10( a). The substrate 130 and charged dots 1010 arethen dusted with positive nanoclusters 140, resulting in the depositionof four individual nanoclusters 1020, as shown in FIG. 10( b). Thesenanoclusters 1020 serve as nucleation sites for nanowire growth, and mayinclude a conductive material, e.g., gold. An gas injection needle 1030,for example, the Gas Injection System (GIS) manufactured by SEI, Corp.may be used to inject a precursor thus initiating growth of nanowires1040 at the nucleation sites defined by nanoclusters 1020, as shown inFIG. 10( c). The precursor may be one of many gases, such as silane(SiH₄), and nanowires many be formed from various materials, e.g.,silicon. An advantage of this approach is that it enables precisecontrol of the size of a nanocluster, and the precise positioning of ananocluster on a substrate, which dictate the quality of thenanotube/nanowire, and the complexity of a three-dimensional functionalstructure, respectively.

The ALD and FIB may be combined with a third technique, ESEM, to createa very thin gap between two structures. Referring to FIGS. 11( a)-(d), aparticle trap 1100 may be created by fabricating a gap 1110 withnanometer precision in a nanostructure 1120. Gap 1110 may be used totrap particles in a fashion similar to that used by Bezryadin et al.,who fabricated platinum electrodes with a spacing of ˜4 nm and were ableto trap a single conducting nanoparticle composed of Pd (see, e.g.,Bezryadin, A., C. Dekker, and G. Schmid, Applied Physics Letters, 1997.71(9): p. 1273-1275, hereby incorporated by reference). In contrast toBezryadin et al., who defined spacing with standard techniques such aselectron-beam lithography and reactive ion etching, gap 1110 is definedby a combination of ALD, FIB, and ESEM. A nanostructure 1120 may beformed on a substrate 1130 using the processes described above withreference to FIGS. 1 to 5, 7 to 9, or another process. Nanostructure1120 may be formed of a metal like platinum (Pt), Cu, or Al; aninorganic semiconductor such as Si, Ge, InP, GaAs; or an insulator suchas silicon dioxide (SiO₂). Substrate 1130 may be formed from aninsulator, such as SiO₂. Subsequently, an ion beam 1140 may mill a gap1135 in structure 1110, with a gap of length l₂ being smaller thaneither a length l₃, width w₂, or height h₁ of nanostructure 1120. Thelength l₂ of gap formed by ion milling depends on the material used innanostructure 1120 and on ion beam milling parameters and is, e.g., onthe order of tens of nanometers. Sections 1150 and 1160 of nanostructure1120 are then coated with second and third monolayers 1170, 1180 usingthe FIB/ALD process as described in reference to FIG. 9, to close gap1130 to a length l₄ that is, e.g., on the order of nanometers. Secondand third monolayers 1170 1180 may be formed of, e.g., elements such asZn, Cd, Hg, Mn, S, Se, Te, and As, or metal oxides such as aluminumoxide (Al₂O₃), tin oxide (SnO₂), or indium-tin oxide (ITO) that exhibithigh conductivity. Finally, a region 1190 of substrate 1130 may beetched with a suitable etchant such as, for example, hydrofluoric acid(HF) to form a first and a second free-standing structure 1192,1194 todefine the particle trap 1100. Particle trap 1100 may be capable ofcreating strong electric fields with very high gradients by theapplication of a voltage between first and second free-standingstructures 1192, 1194. Particles in the proximity of gap 1110 willbecome polarized and may be trapped in gap 1110 or its proximity.

Similar structures with alternating layers of monolayers of nanoclustersand organic molecules may be fabricated without requiring an initialmolecular layer, e.g., gold, to serve as a template. The method forforming such structures is substantially the same as the processdescribed with reference to FIG. 1 or 2, except that, instead ofnanoclusters, organic molecules, e.g., thiols, are dusted and areattracted to the charge layer patterned by the charged beams, e.g., ionor electron beams. Next, inorganic nanoclusters, e.g., gold, adhere tothe organic molecules, e.g., thiols. These steps are repeated to buildstructures of alternating organic and inorganic layers.

More particularly, referring to FIG. 12, a structure 1205 withalternating organic and nanocluster layers may be formed as follows. Aninitial patterned layer 1210, e.g., gold, is defined by, e.g., a processdescribed in reference to FIGS. 1 to 9, 13 or other lithographicprocesses, on a substrate 1220 formed from, e.g., silicon. Organicmolecules 1230, e.g., linear molecules terminated with thiols at bothends, readily form selective bonds with specific inorganic nanoclusters,e.g., gold. These organic molecules 1230 self-assemble onto the initialpatterned layer 1210, creating a monolayer 1235 of organic moleculesthat retains the image pattern of the initial patterned layer 1210. Theorganic monolayer 1235 now has one terminated end group 1237, e.g., athiol, bonded to the initial pattern layer 1210 and another end groupthat is exposed. Next, nanoclusters 1240 that selectively bond to theexposed end of the organic molecule, e.g., gold, are dusted oversubstrate 1220 and adhere to the exposed end groups of the monolayer1235 composed of organic molecules 1230. After global sintering, theprocess of self assembly of organic molecules 1230 and nanoclusterdusting is repeated to produce patterned structures of alternatingmonolayers of nanoclusters 1240, 1240′ and organic molecules 1230,1230′.

The fabrication methods described with reference to FIGS. 1 to 12operate by serial processing. Although the charge patterning process maybe rapid, the process in which energy is transferred to the nanoclustersmay be relatively slow. In certain embodiments, to increase writespeeds, it may be desirable to have a parallel beam process.

In an embodiment, multiple beams may operate in parallel to deliverenergy or deposit charge on a substrate, e.g., 10,000 beams arranged ina 100×100 array. This multiplicity of beams may increase fabricationspeed by many orders of magnitude. The beams may be independentlycontrolled. For example, in an array of laser beams, each laser may bescanned across the surface of a substrate by one micro-mirror in amicro-mirror array. Alternatively, the array of beams may be controlledall together, as in the case of an array of parallel electron beamscontrolled by one set of electromagnetic optics, with pattern controlprovided by on-off control of individual beams within the array,allowing digital control of the resulting pattern.

In one implementation, a parallel array of electron beams may begenerated by an array of light beams directed by a micro-mirror arrayincident onto a photocathode. Such a device may have, for example, a100×100 beam array. The photocathode may be held at a high potentialrelative to the substrate, and an electron beam is generated at eachpoint where light is incident on the photocathode. This beam array maybe focused and scanned by a single set of electromagnetic optics thatcontrols all the beams in parallel. Control of the micro-mirror arrayallows each individual beam to be quickly turned on and off, providing ameans for digital control of the exposure pattern defined by the beamson a substrate. This array of beams may be scanned across the surface ofa substrate, allowing high-speed, high-resolution charge patterning.

More particularly, referring to FIG. 13( a)-(c), multiple electron beams1310 are simultaneously incident in parallel on an electret substrate130, thereby developing a charge pattern 1315. This charge pattern 1315is thus created in a single step rather than by the scanning of a singlebeam across the entire substrate 130 multiple times. A plurality ofpositively charged nanoclusters 140 deposit onto a surface 1327 ofsubstrate 130 and arrange themselves on the charge pattern 1315. Aglobal heating source 1330 heats substrate 130, thereby sintering thenanoclusters 140 to form a continuous structure 1335 that includes thenanocluster 140 material. Global heating source may be, for example, ahot plate or a laser. This process may be scaled up to many thousands ofbeams or more, and therefore the fabrication speed may be increased bymany orders of magnitude.

Referring to FIG. 14, a system 1400 enables the generation of acontrollable array of electron beams 1410 by the use of a light source1420, an array 1430 of micro-mirrors 1440, and a photocathode 1450.Micro-mirror array 1430 may be, for example, a Digital MicromirrorDevice (DMD) array such as Texas Instruments' 0.55 SVGA DDR system.Micro-mirror array 1430 may be used to modulate the illuminating lightsource 1420, e.g., a laser. Photocathode 1450 may be fabricated bydepositing a thin film of gold having a thickness of, e.g., 15 nm onto atransparent substrate and illuminating the gold through the transparentsubstrate. The transparent substrate may be formed of, e.g., quartz andsapphire and may have a thickness of, e.g., 1 mm [See, e.g., X. Jiang,C. N. Berglund, A. Bell, and W. Mackie, “Photoemission from Gold ThinFilms for Application in Multi-photocathode Arrays for Electron BeamLithography,” J. Vac. Sci. Technol., B16, pp. 3374-3376,November/December 1998, incorporated herein by reference]. Light source1420 directs a beam of light 1460 at each micro-mirror 1440 in array1430. The mirrors 1440 tilt to direct the light beams 1460 onto asurface 1417 of the photocathode 1450 directly below mirrors 1430, or todirect beams 1405 away from the photocathode 1450 entirely. When thelight beams 1460 strike the photocathode 1450, the light beams 1460generate electron beams 1410 that are then used in the fabricationmethods described with reference to, e.g., FIGS. 1, 4 to 7, 10, 12 and15 to 17. System 1400 allows precise digital control of a large array ofelectron beams 1410.

The nanostructure formation methods described above with reference toFIGS. 1 to 14 may also utilize direct feedback to ensure accuracy in thefabrication of functional structures. Feedback may be introduced atdifferent stages of processing. It may either be done directly after theformation of the charge pattern or after nanocluster deposition. Forexample, after a charge is written, a voltage contrast image of thesubstrate may be obtained. Errors in charge placement due to a firstbeam may be removed by discharging the errors with a second beam ofopposite charge polarity. The first beam may be an electron beam and thesecond beam may be a positive ion beam. In an embodiment, the energybeam may be a laser. In another embodiment, input for feedback may be animage that communicates topography of the built structure, for example,an image taken with an SEM, which is compared to the desired structurevia computer vision algorithms. Alternatively, input for feedback may befrom a collection of composition-specific data, for example, an energydispersive x-ray (EDX) detector, where the detector returns the identityof the element or elements from which the structure is formed. Anelemental map of the formed structure may also be combined with atopographical map and compared to the desired structure. In anotherembodiment, input for feedback may be an excitation of the nanoclustersthat induce optical emission, such as electroluminescence (EL) (seee.g., Lee, T.- H. and R. M. Dickson “Single-Molecule LEDs from NanoscaleElectroluminescent Junctions.” Journal of Physical Chemistry: ACS ASAPincorporated herein by reference) which may be then collected viasensitive charged couple devices (CCD).

After comparing data collected from various sources, which may be, forexample, a map collected via an EDX detector, an SEM image, an FIBimage, and/or a CCD image that may be used to pinpoint the position andcomposition of nanoclusters via EL, to the desired data corresponding toan ideally built structure, a computer algorithm may compute the stepsrequired for correction of the structure, if there are anydiscrepancies, and the necessary corrections may be performed. Thecorrections may be additive (when part of the structure needs to becreated), subtractive (when part of the structure needs to be removed)or both (when dealing with complex corrections of three-dimensionalstructures). One embodiment of the subtractive corrections may employion beam etching, for example, with an FIB. Any of the methods mentionedpreviously with reference to FIGS. 1 to 8, 10, 12 and 13 may be used toperform additive corrections.

The feedback process enables high-yield through error-detection anderror-correction. A voltage contrast image of the substrate may be takenafter charge patterning the substrate. Errors in charge absence may becorrected by recharging regions that should have been charged accordingto the original pattern. In another form, a positive ion beam may beused to charge the substrate and an electron beam may be used for thesubsequent error correction.

Referring to FIG. 15, an error in a charge pattern may be corrected asfollows. An electron beam 1510 writes a charge pattern 1520 on substrate130, with an error 1530 of missing charge. Electron beam 1510 can beused to correct error 1530 by adding a negative charge to the spot 1530where a charge is missing. An error of misplaced charge 1540 may becorrected by neutralizing the misplaced charge 1540 with a positivecharge 1550. A positive ion beam 1560 may be used to generate thepositive charge 1550.

Referring to FIG. 16, a feedback system 1600 enables the correction oferrors immediately after the definition of a charge pattern or after thedusting the substrate with nanoclusters. An electron beam 1605 isemitted from an SEM 1610, and is incident on a nanostructure 1620.Nanostructure 1620 may be a nanoelectronic device or a portion thereof,that includes first and second features 1622, 1624. First and secondfeatures 1622, 1624 may vary in composition and in dimension.Nanostructure 1620 may be formed, for example, using the fabricationmethods described above, e.g., with reference to FIGS. 1 to 15. Whenelectron beam 1605 collides with a surface 1626 of feature 1622,secondary electrons 1635 and x-rays 1640 are emitted. The number ofemitted secondary electrons 1635 depends on the topography and, to alesser extent, on the composition of the feature 1622. For example, anedge is generally relatively easily discernable as the secondaryelectron count is generally high for edges of structures. The wavelengthof x-rays emitted depends solely on the composition of feature 1622,making it possible to create an elemental map of the nanostructure 1620including first and second elements 1622, 1624. The data correspondingto topography may be collected by a secondary electron detector (SED)1645, and elemental data may be collected by an energy dispersive x-ray(EDX) detector 1650, e.g., an EDAX Phoenix EDS X-ray microanalysissystem. Feedback input parameters are not limited to detectors 1645,1650. Other embodiments of collected data, for example, may include aCCD image corresponding to electroluminescence of the particles thatcompose the nanostructure 1620 under an applied electromagnetic field.

The data collected from detectors 1645, 1650 may be correlated andanalyzed by computation system 1655 that includes one or more computerswith associated software and hardware. Computation system 1655 comparesthe data collected to data relating to a desired nanostructure 1660 withdesired first and second features 1662, 1664 corresponding to thefabricated features 1622, 1624. If computation system 1655 determinesthat a processing error has occurred, it may provide feedback in anumber of ways. If an additive correction has to be performed,computation system 1655 may, for example, send a signal to clustersource 1660 to generate nanoclusters 140, and also send signals to SEM1610 and FIB 1665 to deposit the required charge needed to repair thenanostructure 1620 by addition of nanoclusters. If a subtractivecorrection has to be performed, computation system 1655 may, forexample, send a signal to FIB 1665 to remove material from thenanostructure 1620. Thus the feedback loop is closed between the actualnanostructure 1620 and desired nanostructure 1660, and the process maybe repeated until the desired functional structure is formed.

In an embodiment, cluster by cluster feedback fabrication enables highlyprecise processing. Cluster by cluster feedback fabrication utilizes abeam with an electrostatic apparatus capable of placing single charges,a cluster source with mass quadrupole or other electrostatic filter thatcan select a single cluster, and a feedback system that detects theplacement of that cluster at the region of the deposited charge. Thefeedback system may utilize the processing elements discussed withreference to FIGS. 15 and 16, and instruct the single-cluster deliverysystem to eject another cluster of appropriate mass and charge to thecharge pattern if the initial cluster placement is inaccurate. The writeand dust procedure may employ alternating between charging and dusting,as discussed with reference to FIGS. 5( a)-5(b).

To implement the above-described feedback scheme in parallel with anarray of charged beams, each beam may have its own associated detectoror detectors 1645, 1650.

To analyze the composition of nanostructures such as, for example,nanostructure 1620, a combination of analysis of x-rays 1640 with EDXand milling with FIB 1665 may be used. EDX may be used for elementalanalysis of regions of micron dimensions. Although EDX is generally usedto obtain elemental information for a planar region, it may be extendedto analyze successively milled planes, thus reducing the limit ofresolution to the minimum amount of material that can be milled usingthe FIB. After successive planes are analyzed, the data may be combined,for example, by mapping elemental data to various colors to form ahigh-resolution three-dimensional image of the sample. This process,although destructive in nature, may be combined with other methods ofplanar analysis to produce a high-resolution image rich in content toprovide, e.g., detailed data regarding the composition ofnanostructures.

Referring to FIG. 17, a fabrication system 1705 may be used to enableeach of the fabrication steps described with reference to FIGS. 1 to 16to be carried out under a single vacuum. Fabrication system 1705 maycombine a number of components, including a deposition chamber 1710, abeam source 1715, an MSSBB source 1720, and vacuum pumps 1725. In someembodiments, an NSBB source may be used instead of MSSBB source 1720.Beam source 1715 may be, e.g., a parallel or singular charged beamsource such as an electron- or an ion-beam. Fabrication system 1705 mayalso include a mass and charge selection apparatus 1730 in fluidcommunication with the MSSBB source 1720. All of these components may bemaintained under a high vacuum, e.g., 10⁻¹⁰-10⁻³ Torr. Feedbackmonitoring system 1735 includes computation system 1655, as well ascustom feedback software written in a programming language such as, e.g.C, and custom hardware input-output (I/O) boards (not shown), a singleor multiple detectors 1740, such as, e.g. an SED or EDX detector, andelectrical connections 1745. Electrical connections between computationsystem 1655 and, for example, the beam source 1715 may be an electricalconnection to the X-Y controllers of the scan coils (not shown) thatcontrol the scanning of beam source 1715; the connection to the MSSBBsource 1720 may be to the power supply that regulates sputtering suchas, e.g., a Glassman DC power supply LV-600 (not shown); the connectionof feedback monitoring system 1735 to selection apparatus 1730 may be toa power supply (not shown) that initiates mass and charge filtering.Feedback monitoring system 1735 monitors fabrication processes occurringwithin fabrication system 1705.

Deposition chamber 1710, containing the beam source 1715, is constructedto allow appropriate vacuum connections to be formed between depositionchamber 1710 and the mass and charge selection apparatus 1730. Asuitable deposition chamber for use as deposition chamber 1710 may bethe XL-30 chamber of a Strata™ DB235 made by FEI Co., or a chamber fromMDC Vacuum Corporation such as the Surface Science Analysis Chamber200000 modified to include beam source 1715. Substrates such assubstrate 130 (not shown) may be mounted on stage 1750 within depositionchamber 1710, where the fabrication of features occurs. Stage 1750 maybe a five-axis stage that is standard in the XL-30 chamber of a Strata™DB235 made by FEI Co., or a laser interferometer stage such as a RaithHigh Precisions Laserstage.

Deposition chamber 1710 may be modified, for example, by the machiningof an adapter plate 1755, including an adapter flange 1760, and a valve1765. Valve 1765 may be a gating valve or a high speed shutter, e.g.pneumatic 8″ Gate Valve 303019 from MDC-Vacuum Corporation. In anembodiment without mass and charge selection apparatus 1730, adapterplate 1755 may be machined to MSSBB source 1720. Adapter flange 1760 maybe, for example, an 8″ conflat flange.

MSSBB source 1720 may be a nanocluster source, e.g. NC200U NanoclusterSource available from Oxford Applied Research. Mass and charge selectionapparatus 1730 may be, for example, a mass quadrupole filter, e.g. QMF20Mass Quadrupole filter available from Oxford Applied Research. Selectionapparatus 1730 is attached to MSSBB source 1720 by appropriate vacuumfittings, e.g., a conflat 8″ flange.

The feedback monitoring system 1735 may perform data manipulation andalgorithms that deduce from input data from one or more detectors 1740,e.g., a SED detector, whether an error has occurred in the fabricationof a nanostructure in deposition chamber 1710. Detector 1740 may also bean EDX detector or CCD for electroluminescence detection. Suchcomponents may be placed within the deposition chamber 1710. If an errorhas occurred during nanostructure fabrication, the feedback softwareinstructs the hardware I/O board to send an appropriate signal to MSSBBsource 1720 to start nanocluster production, followed by a signal toselection apparatus 1730 to select clusters of specific charge, mass andvelocity, as calculated by the algorithm software. This is followed by asignal to the beam source 1715 to scan a beam in a specified manner torepair the error that has occurred, e.g., the repair may be as describedin reference to FIGS. 15 and 16.

Fabrication system 1705 may be maintained at a vacuum by vacuum pumps1725. Vacuum pumps 1725 may include turbomolecular pumps and roughingpumps. Vacuum pumps 1725 are capable of maintaining a high vacuum, e.g.,10⁻¹⁰-10⁻³ Torr, in deposition chamber 1710, beam source 1715, selectionapparatus 1730, and MSSBB source 1720. Vacuum gauges such as a coldcathode gauge or ion gauge (not shown) may be placed throughout thefabrication system 1705 to monitor pressure.

Additional components may also be incorporated into fabrication system1705, such as a quartz crystal monitor 1770 to monitor MSSBB depositionrates, a global heat source such as a laser 1775 to sinter patternedparticles, additional gas deposition needles 1780 for introduction ofgases such as those described with reference to FIGS. 6, 9 to 11,electrostatic components 1785 described with reference to FIGS. 4(a)(c), a channeltron (not shown) or additional detectors 1740 to beutilized in feedback monitoring system 1735. Each of these componentsmay be added to deposition chamber 1710 through vacuum ports availablein, for example, the XL-30 chamber of a Strata™ DB235 made by FEI Co.,or through ports of a custom-built chamber. Each of these components isalso in electrical communication with computation system 1655.

Fabrication system 1705, including all components of feedback monitoringsystem 1735 for fabrication of nanostructures, may be operated asfollows. First, a substrate such as substrate 130 is introduced intodeposition chamber 1710 and mounted onto stage 1750. In one embodiment,the deposition chamber 1710 may be at atmospheric pressure duringloading, and substrate 130 may be mounted manually. In anotherembodiment, deposition chamber 1710 may already be at a vacuum, andsubstrate 130 may be introduced via a load lock (not shown).

Feedback monitoring system 1735 may be used to automate fabricationsystem 1705 as well as to monitor feedback during fabrication ofnanostructures. After substrate 130 is mounted on stage 1750, feedbackmonitoring system 1735 may initiate the use of vacuum pumps 1725. Vacuumpumps 1725 may pump down deposition chamber 1710, selection apparatus1730, and MSSBB source 1720. In some embodiments, MSSBB source 1720 andselection apparatus 1730 may already be maintained at a high vacuum,because the shutter or gate valve 1765 may be kept closed except duringdeposition. MSSBB source 1720 and selection apparatus 1730 may be ventedto atmosphere for maintenance and similar such tasks.

After a suitable vacuum is achieved in deposition chamber 1710, MSSBBsource 1720 and selection apparatus 1730, e.g., 10⁻⁶ Torr, the beamsource 1715 and other additional components such as detectors 1740,electrostatic components 1785, and quartz crystal monitor 1770, may besimilarly initiated by the feedback monitoring system 1735. At thispoint, custom automation software may be launched to initiate thefabrication of a nanostructure in deposition chamber 1710. Thisnanostructure may be designed by custom software similar to AutoDeskInventor or DesignCad, where the structure and composition of thenanostructure are indicated.

After the automation software is launched, fabrication may proceed asdescribed, for example, with reference to FIG. 1( a)_(c). Morespecifically, the feedback system 1735 may direct the beam source 1715to write charge pattern 120 (not shown) into substrate 130. Next, thefeedback monitoring system 1735 may check to determine if the chargepattern 120 was written properly. Error detection and correction of thecharge pattern may be carried out as described with reference to FIGS.15 and 16.

After the desired charge pattern 120 is written, the feedback monitoringsystem 1735 may direct the MSSBB source 1720 to introduce, for example,a stream of MSSBBs or nanoscale building blocks such as nanoclusters 140(not shown). Then, feedback monitoring system 1735 may initiate theselection apparatus 1730, which may begin to filter nanoclusters 140 fora pre-determined mass and charge. Gate valve or high-speed shutter 1775may also be opened by feedback system 1735 at this time. Nanoclusters140 may then be introduced into deposition chamber 1710 and may, forexample, reach a low velocity due to interaction with electrostaticcomponents 1785. At this point, the nanoclusters may be attracted by andadhere to the charge pattern 120. The feedback system 1735 could thenverify that the nanoclusters 140 were placed properly, and could makemodifications as described with reference to FIGS. 15 and 16 to correcterrors. After nanoclusters 140 are properly placed on charge pattern120, feedback monitoring system 1735 may initiate the global sinteringof particles using laser 1780. This process may be repeated layer bylayer until the desired nanostructure is constructed.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativerather than limiting on the invention described herein. The scope of theinvention is thus indicated by the appending claims rather than by theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A method for forming a structure, the method comprising: introducing a plurality of at least one of molecular-size scale and nanoscale building blocks to a region proximate a substrate; and simultaneously scanning a pattern on the substrate with an energy beam, wherein the energy beam causes a change in at least one physical property of at least a portion of the building blocks, such that a probability of the portion of the building blocks adhering to the pattern scanned by the energy beam is increased, and wherein the building blocks adhere to the pattern to form the structure.
 2. The method of claim 1, wherein the energy beam comprises at least one of an electron beam and an ion beam.
 3. The method of claim 1, wherein the change in the physical property is caused by a direct collision between the energy beam and the portion of the building blocks.
 4. The method of claim 1, wherein the change in the physical property is sintering together of the building blocks.
 5. The method of claim 4, wherein the energy beam sinters the portion of the building blocks by heating at least a portion of the substrate proximate the portion of the building blocks.
 6. The method of claim 1, wherein the building blocks are selected from the group consisting of ions, nanoclusters, nanoparticles, and organic molecules.
 7. The method of claim 1, wherein the building blocks comprise nanoclusters.
 8. The method of claim 7, further comprising a step of globally sintering the adhered nanoclusters together, forming the structure as a locally solid pattern.
 9. The method of claim 8, wherein the sintered-together nanoclusters form a monolayer.
 10. The method of claim 1, wherein the building blocks are introduced by dusting.
 11. The method of claim 1, wherein the building blocks are introduced by directing them toward the substrate as a stream.
 12. The method of claim 11, further comprising: controlling a velocity of the plurality of building blocks.
 13. The method of claim 12, wherein the velocity of at least a portion of the plurality of building blocks is reduced in the region proximate the substrate.
 14. The method of claim 12, wherein the velocity of at least a portion of the plurality of building blocks is controlled by an electric or magnetic field.
 15. The method of claim 12, wherein the velocity of at least a portion of the plurality of building blocks is controlled by a charged aperture disposed near the substrate.
 16. The method of claim 1, wherein the energy beam and at least a portion of the building blocks interact by electrostatic interaction.
 17. A method for forming a structure, the method comprising: introducing a plurality of at least one of molecular-size scale and nanoscale building blocks to a region proximate a substrate; and simultaneously scanning a pattern on the substrate with an energy beam, wherein the energy beam and at least a portion of the building blocks interact by electrostatic interaction, and wherein the building blocks adhere to the pattern to form the structure.
 18. The method of claim 17, wherein the energy beam comprises at least one of an electron beam and an ion beam.
 19. The method of claim 17, wherein the building blocks are selected from the group consisting of ions, nanoclusters, nanoparticles, and organic molecules.
 20. The method of claim 17, wherein the building blocks are introduced by one of dusting or directing them toward the substrate as a stream. 